The present invention relates to an image forming apparatus such as a copying apparatus or the like, and especially to an image forming apparatus such as a front loading type apparatus in which small size, low cost and high performance are pursued.
Generally, when copying is conducted by a copying apparatus, a margin is intentionally provided on the leading edge portion of a transfer paper. This is because a transfer paper is wound around a portion of a fixing section of the apparatus when an image exists on the leading edge portion, and there is a high probability that jamming occurs.
In the small and low cost copying apparatus described above, there is an apparatus in which a white plate is provided in the position corresponding to the leading edge of a document, under a document tray so that a margin can be made. There is another technique in which the movement of an optical system after its scanning operation has been started, is detected by a sensor, which triggers an LED for erasing, and the margin is made by erasing a charge on the surface of a photoreceptor.
In the technique in which the aforementioned white plate is provided, there are problems in which an erased amount is changed depending on a copying magnification, or a mechanical shadow occurs.
In the technique in which the margin is made by using the LED for erasing, there is a problem in which confirmation of a position of an optical system is difficult, and therefore, stabilization of an operation to erase a leading edge of an image is difficult, in small sized apparatus. That is, in the small sized apparatus, it is required to limit a width to a minimum in order to reduce installation space, or to speed up starting of an optical scanning operation in order to obtain high performance. In the case where an operation timing of the LED for erasing is determined after the sensor has detected the position of the optical system, the timing of the erasing operation is too late, because a sliding distance of the optical system from the start of its scanning operation to its arrival at a leading edge of a document is short. Further, even when the operation timing can be obtained, there is a case where a stable margin can not be made since the position of the optical system at the time is fluctuated by the influence of undershooting or overshooting at the time of start-up.
In the case described above, it is considered that the operation of the optical system can be precisely controlled by using many ICs, and thereby fluctuation can be prevented. However, this results in the apparatus becoming complicated and of high cost.